1. Field of the Invention
This invention concerns a magnetic alloy for use in magnetic heads and, particularly, it relates to an amorphous alloy main composed of Co for use in magnetic heads.
2. Description of Prior Art
Crystalline metal materials such as permalloy and sendust, as well as oxide materials such as Mn-Zn ferrite and Ni-Zn ferrite have mainly been used for magnetic head materials. Although crystalline metal materials have a saturation magnetic flux density higher than that of ferrite (oxide materials), since the specific resistivity of the former can be under 100 .mu..phi..cm, the magnetic permeability is very low in the frequency region used in video tape recorders or the like (MHz order).
On the other hand, since ferrites have a high specific resistivity, exhibit excellent electromagnetic conversion properties in the higher frequency region and, further, show an excellent abrasion resistance, Mn-Zn type ferrites have been used mainly for video heads. However, ferrites have low saturation magnetization, which results recording distortion and increased noise.
In the high density recording, a high frequency band is generally used. Accordingly, it is necessary to form the core materials used in high density magnetic heads into a thin film or the specific resistivity .rho. thereof needs to be increased in order to prevent degradation of the magnetic permeability due to eddy current loss. Although sendust material has a large saturation magnetization and higher specific resistivity as compared with that of permalloy, it is fragile and, accordingly, can not be formed into a thin film.
Recently, excellent magnetic and mechanical properties have been found in amorphous alloys having no crystalline structure. That is, since the amorphous alloys have no crystalline structure, their specific resistivity .rho. is several times higher than crystalline metal alloys and they have low coercive force and high magnetic permeability due to the absence of crystal magnetic anisotropy. Further, the Vickers hardness is about 1000, which is higher than that in crystalline metals.
Furthermore, a composition capable of reducing magnetic distortion to near zero has almost been formulated and a study has now been made on how to apply it in magnetic head core materials.
However, in using such amorphous alloys in magnetic head cores for use in the high density recording, it is necessary that they have a high magnetic permeability in the high frequency region above 1 MHz as well as in the lower frequency region. In view of the above, it is necessary to satisfy the following requirements:
(1) high specific resistivity, PA0 (2) high initial magnetic permeability, PA0 (3) high abrasion resistance, PA0 (4) high thermal stability, PA0 (5) high corrosion resistance.
The present inventors have found that amorphous alloys capable of satisfying all of the foregoing requirements (1) through (5) occur within an extremely narrow composition region.
This invention discloses such a composition region capable of satisfying all of the above requirements 1 through 5, in an amorphous alloy consisting essentially of four elements, Co, Fe, Si and B, to which Cr is added for providing corrosion resistance and Ru is added for improving abrasion resistance and in which secondary phase particles are dispersed throughout the alloy matrix.